Refactor the CLI, part 2

[fghaas]

Eventually, we're going to want olx to do more than just create a new run. Thus, implement subcommand functionality and make a few more related changes:

• Turn olx-new-run into olx new-run, retaining the previous syntax as a compatibility alias.
• Also retain new_run.py, but add a user-facing FutureWarning.
• Use unicode literals everywhere.
• Improve the unit tests.

[codecov-io]

Codecov Report

Merging #28 into master will increase coverage by 1.82%. The diff coverage is 87.83%.

@@            Coverage Diff             @@
##           master      #28      +/-   ##
==========================================
+ Coverage   85.21%   87.03%   +1.82%     
==========================================
  Files           6        6              
  Lines         284      324      +40     
==========================================
+ Hits          242      282      +40     
  Misses         42       42

Impacted Files	Coverage Δ
tests/test_cli.py	100% <100%> (ø)	:arrow_up:
tests/test_helpers.py	100% <100%> (ø)	:arrow_up:
olxutils/templates.py	100% <100%> (ø)	:arrow_up:
olxutils/helpers.py	73.68% <60%> (+0.71%)	:arrow_up:
olxutils/cli.py	68% <83.33%> (+7.5%)	:arrow_up:

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